Use of knockout and transgenic mouse models in disc research

The intervertebral disc is a fibrocartilaginous structure that is located between two vertebral bodies; it transmits loads through the spine and allows bending, flexion, and torsion of the column. The intervertebral disc consists of an outer ring of fibrous cartilage called the annulus fibrosus and an inner gelatinous structure, the nucleus pulposus. The nucleus pulposus is a gelatinous structure mainly formed by sparse chondrocyte-like cells embedded in a highly hydrated aggrecan-containing gel (Raj 2008). For more details of the structure of the disc, see Chaps. 4 and 5. The annulus fibrosus is composed of an outer layer of collagen I and an inner region containing collagen II. The collagen fibers are arranged in parallel lamellae, and elastin fibers are interposed between the lamellae.